In recent years, there has been increasing interest in utilizing biogas as a renewable energy source. The utilization of biogas has two significant benefits: (1) averting greenhouse gas (GHG) emissions, and (2) providing alternative energy resources to mitigate the dependency upon non-renewable fuels, e.g. oil and coal. As such, complete and efficient utilization of readily available biogas is attractive as the demand for energy increases.
Landfill biomass, which is approximately 67% municipal solid waste (MSW), anaerobically decomposes in landfills to provide renewable methane-containing gases (RMG) that are important resources for alternative energy. Other sources of renewable methane-containing gases include digester biogas that is generated by anaerobic digestion or fermentation of animal, agricultural, and other types of biodegradable wastes. However, landfill gases (LFG) may be understood as being more abundant than digester gases.
The constituents of landfill gases are typically methane (20-60%) and carbon dioxide (22-60%). Additionally, landfill gases contain nitrogen (10-15%), oxygen (0-5%), other trace compounds, and are saturated with water vapor. However the composition may vary depending on the type of waste and the age of the landfill. The high methane content makes landfill gas a desirable energy source.
Carbon dioxide may be removed from landfill gas using available technologies, e.g., amine-scrubbing, cryogenic absorption, selective adsorption, membrane separation, etc., and the resulting methane, called biomethane, can be used as a substitute for natural gas (NG). For low BTU applications (≦500 btu/cf), carbon dioxide in LFG is not typically removed. Instead, with improvement in engine designs, the majority of reciprocating engines for power generation in use today operate without removal of carbon dioxide in landfill gas, e.g., Caterpillar G3520 or GE Jenbacher Types 2-6.
However, from a chemical standpoint, a significant challenge of using landfill gas for low BTU operation is in the area of contaminants, which can be detrimental to the engines by causing corrosion, erosion, fouling, etc. As such, frequent maintenance or repairs are needed causing unwanted interruption of electricity generation and increases in operating costs.
Cost effective technologies for removing these contaminants are needed for future use of low BTU applications. The requirements are equally important in high BTU applications
(>500 btu/cf) in which, in addition to the removal of CO2, nitrogen and oxygen in the LFG must be removed to meet the pipeline specification, e.g., <4% nitrogen and <0.2% oxygen.